Combustion control device



Patented Apr. 11, 1944 COMBUSTION CONTROL DEVICE Siegfried G.Isserstedt, Minneapolis, Minn., as-

signor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, acorporation of Delaware Application December 22, 1941, Serial No.423,990

19 Claims. (01. 158-28) The present invention relates broadly toautomatic control devices for systems for controlling the combustion offluid fuel. More specifically, the invention relates to an automaticcontrol device for use in combination with an extremely sensitivecombustion responsive device wherein a timing unit, such as a thermaltimer, is utilized for the purpose of timing the, trial ignition Period,the post ignition timing, and the time required for the system torecycle following a flame failure or a normal shut-down.

It has been found that in order to accurately predetermine the timerequired for a thermal timer to heat up and perform a control functionsuch as the operation of a switch, that it is necessary to put arelatively large amount of heat into the thermal element, This has anobvious disadvantage where the heat is put into the thermal timercontinuously during therunning of the system because it will require avery long time for the timer to return to its cold position after thesystem has been shut down.

amount of heat is put into the thermal timer to cause the timer toperform its proper control functions and place the system in runningcondition, and thereafter reduce the amount of heat put into the timerto an amount justsumcient to cause the timer to take the desired timeers for causingv the device to move toward its safety position upon anoriginal call for heat and to reverse its movement and move toward itsrunning position following the establishment of combustion, providingcombustion takes place before it has reached its position of safety. Afurther object is to provide the thermal timer unit with a startingswitch which is opened when the timer is in its running position andwhich prevents the 'reenergization of the burner motor following ashut-down until the timer has had a chance to cool and return to itsoriginal position. I

These and other object will readily become apparent as the following'specification is read in the light of the accompanyingdrawing, the

singie figure of which diagrammatically illus-" trates an automatic,burne'r' control system embodying the various features of my invention.

The reference numeral l0 indicates a thermostat which is adapted to belocated in the space being controlled by the burner of my automaticcontrol system. This thermostat is shown as comprising a bimetallicelement II which is fixed at one end and which carries at its free end aflexible contact blade l2 and a second contact blade I3. Upon a decreasein temperature the resilient contact blade l2 first engages thestationary contact l4 and then on a further decrease in temperature thecontact blade Hi engages the stationary contact l5.

interval to return to its cold condition after the control system hasbeen shut down. -In this way I am enabled to take advantage of theimproved operation of the timer due to the large amount of heat put intoit and at the same time I do not get the disadvantage of the long timerequired for the timer to cool down after the system has been shutdown.

A further object of the invention is to provide a single thermal timerunit for timing the trial ignition period, the post ignition period, andthe scavenger period. A further object of the invention is to make thisthermal timer unit in the form of a thermal device anda latch whichcooperates therewith, the latch having a starting position, a safetyposition, and a running position, and to additionally provide anelectromagnetic relay which controls the burner motor and Which alsoacts to relatch the latch when it is in its running position but whichis inoperative to relatch the latch when it is in its safety position.

A still further object of the invention is to provide the thermal devicewith a series of heatso Th r i notch 22 is rel ively shallow with ,l

The reference numeral" indicates generally the thermal timer unit of myinvention which is shown as comprising a pair of bimetallic blades i8and I9 which are fixed at their lower ends and free at their upper ends,the upper ends moving toward the right on heating as indicated by thearrows. .The upper end of the blade I8 pivotaliy carries a latch member20 which has a latching surface-2| which rests upon the free end of theblade l9 when the two blades l8 and I9 are cold. The latch 20 isprovided with a pair of shoulders which form what will be referred to asa running notch 22"and a safety notch 23. It will be seen that if theblade l8 warps more rapidly to the right than the blade 19, that thelatch 20 will move to the right with I respect to the blade l9 and therunning notch 22 will drop down onto the free end of the blade l9. Onthe other hand, if the blade I9 warps more rapidly than the blade l 8,then the latch 20 will move to the left with respect to the blade I9with the result that the safety notch 23 will drop down onto the freeend of the blade l9.

respect to the safety notch 23 and therefore when the blade I8 is in therunning notchthe latch 20 will drop down arelatively short distance fromthepositionshown in thedrawing and when the blade|9 is in the safetynotch the latch 20 will drop down a considerably greater distance.

The latch 20 is adapted to control a pair of switches, one of whichcomprises the twocontact blades 25 and 26 and the other of whichcomprises the two contact blades 21 and 28. Both of these switches arebiased toopen position but when the latch is in its latched position asshown in the drawing, the stem 29 holds the contact blades 25 and 26 inclosed position and the stem 30 holds the contact blades 21 and 28 inclosed position. When the free end of the bimetal blade H! is in eitherthe running notch 22 or the safety notch 23 the latch 2m will drop downfar enough to permit the contact blades 25 and 21 to move open circuitposition. Therefore, the only time that these two switches are in closedposition is when the latch 20 is in its latched position as shown in thedrawing with the free end of the blade |9 supporting the latch 20 bymeans of the latching surface 2|.

The latch 20 operates a third switch which is comprised of the resilientcontact blades 3| and 32. Unlike the other two switches, this switch isbiased to closed position. With the latch 20 in latched position asshown in the drawing, the switch 3|, 32 is closed but when thebimetallic blade I9 is in the safety notch 23 the latch drops far enoughto permit stem 33 to drop down and engage the extended end of contactblade 3| and move it to open circuit position. When blade I8 is in therunning notch 22 the latch 20 does not drop down far enough to permitthe stem 33 to open the switch 3|, 32. Therefore, this switch is openwhen the bimetallic blade I! is in the safety notch but is closed whenthe blade I9 is in the running notch 22 when the latch 20 is in thelatched position as shown in the drawing.

The electric heater 351s positioned to heat the bimetallic blade l9 andelectric heaters 36 and- 31 are adapted to heatthe bimetallic blade IS.The bimetallic blade |9 carries a pair of resilient contactblades 4|)and 4|, these blades being insulated from each other and from thebimetallic blade l9 by means of the block of insulation 42. The contactblades 40 arid 4| are adapted to cooperate respectively with the twocontacts 43 and 44 which are carried by, and electrically connected to,the bimetallic blade IS. The two contact blades 40 and 4| are adapted tobe operated by means of a stem 45 carried by the bimetallic blade |8, sothat when the two bimetallic blades l8 and I9 move relatively closertogether from the position shown in the drawing, the insulated end ofthe stem 45 will first force the contact blade 4| out of engagement withcontact 44 and then the insulated button 46 on the contact blade 4| willforce the contact blade 40 out of engagement with contact 43.

My control system is provided with an electromagnetic relay having arelay winding 48 which controls an armature indicated by the dotted line49. The relay winding 48, when energized, is

adapted to raise the armature 49 which in turn -moves the switch arms50, 5|, 52 and 53 from the position shown in the drawing. intoengagement with the stationary contacts 54, 55, 56 and 51 respectively.When the relay winding 48 is cleenergized, this armature movesdownwardly again due to the action of gravity and if desired, thismovement may be aided by means of a spring diagrammatically illustratedat 58. The pivoted switch arm 50 is provided with an extension 88 whichin the out" position of the relay as shown in the drawing, engages thefree end 6| of the latch 20 and holds it in its raised position inwhichall of the switches controlled by this latch are in closed position andthe latching surface 2| is reset on the end of bimetallic blade l8. Whenthe relay winding 48 is energized and the armature 49 pulled in, theextension 60 is withdrawn from the latch 20 and moved to the dotted lineposition in which the latch 20 is adapted to move either to its runningposition or to its safety position, depending upon whether thebimetallic blade I 9 is in the running notch 22 or the safety notch 23.When the blade I9 is in the running notch 22, the latch 20 movesdownwardly only a slight distance so that when the relay 48 is againdeenergized, the extension 60 will engage the free end 6| of the latch20 and return it to the position shown in the drawing so that when theblade I9 returns to its cold position it will again hold the latch 20 inits latched position. However, when the blade -|9 is in the safety notch23 the latch 20 has lowered to such an extent that the extension 60passes above the free end 6| when the relay winding 48 is energized,therefore, the operation of the relay can have no effect upon the latchunder these conditions.

In order to return the latch 20 to its latched position when thebimetallic blade I9 is in the safety notch 23, a manual push button 62has been provided. If it is desired that this manual reset-be madetrip-free, the button 62 may be mechanically connected, as shown by thedotted line, to open the switch 63 during the resetting operation of thelatch. In this way it will be impossible to manually maintain the burnermotor circuit in closed position when it would otherwise be in opencircuit position, .by means of the manipulation of the manual resetbutton 62.

Any type of device for delivering fuel to a burner, such as an oilburner motor, has been illustrated diagrammatically at 65. 66 indicatesa device for igniting the fuel delivered by the motor 55. Indicatedgenerally at 61 is a device which is adaptedto respond to the combustionof the fuel delivered to the burner by motor 65. This device is adaptedto operate a switch arm 68 into engagement with a stationary contact 69upon the establishment of combustion. This combustion responsive devicemay be the usual slipfriction type of switch mechanism or any other typeof mechanism which will close the switch 68, 69 in the presence ofcombustion and open this switch in the absence of combustion, it beingpreferred that the switch is not calibrated but will respond totemperature changes.

The control system is powered from the supply lines 10 and 1| to whichthe primary winding 12 of a step-down transformer 13 is connected bymeans of the conductors 14 and 15. Transformer 13 is provided with asecondary winding 16.

Operation The various elements of my control system are shown in thepositions which they assume when the room thermostat I0 is satisfied andtherefore in open circuit position. It will be noted that the bimetallicblades l8 and I9 are in their cold condition and therefore the latch 20is in its latched position in which the three switches 25,

26; 21, 23, and 3|, 32 are closed. There is no combustion. at the burnerand therefore the combustion responsive switch 88, 69 is in open circultposition. At this time the relay winding 48,

the burner motor 65, and the ignition device 56 will be deenergized.

Under these conditions the temperature in the room in which thethermostat I is located will begin to fall and the resilient blade I2will first engage the stationary contact I4. This will not result in theestablishment of any circuit at this time due to the fact that the relayswitch arm 50 is separated from its stationary contact 54. A furtherdecrease in room temperature will cause the switch blade I3 to engageits stationary contact l5 and this will result in the energization ofthe relay winding 48 through the following circuit: from one side of thesecondary winding 16 of the transformer 13 to conductor 80, contact I4,switch blades I2 and I3,contact I5, conductors 8|, 82 and 83, electricheating element 35, conductors 84 and 85, switch blade 4|, contact 44,bimetallic blade I9, conductors 8B and 31, relay winding 48, conductor88, switch blades 32 and 3|, conductor 89, switch 63, and conductor 90back to the other side of the secondary winding 15. The above circuitnot only energizes the relay winding 48 but'also energizes the electricheating element 35 which heats the bimetallic blade I9. Energization ofthe relay winding 48 pulls in the armature 49 which causes the switcharms 50, 5|, 52 and 53 to move into engagement with their stationarycontacts 54, 55, 56 and 51, respectively, and also causes the extension60 on the switch arm 50 to move from beneath the end 6| of the latch 20to place this latch under the control of the relative movements of thetwo bi- V metallicblades I8 and I9.

Movement of the relay switch arms 50 and 5| into engagement with theirstationary contacts 54 and 55 sets up the following holding circuit forthe relay winding 48 and the electric heating element 35: from one sideof the secondary winding 16 through conductor 80, contact I4, switchblade I2; bimetallic element II, conductor 92, contact 54, switch arm50, conductors 82 and, 83, electric heating element 35, conductors 84and 93, contact 55, switch arm 5|, conductor 94, switch blade 40,contact 43, bimetal blade I9, conductors 86 and 81, relay winding 48,conductor 88, switch blades 32 and 3|, conductor 89, switch. 63 andconductor back to the other side of the secondary winding 16. It will benoted that this holding circuit is independent of the last to closeswitch I3, I5 on the room thermostat I0 and 4|, 44 on the bimetallicblade |9. 'I'hese switches do not make as firm a contact as the first toclose switches I2, l4 and 40, 43, and therefore a holding circuitindependent of them is desirable.

Engagement of switch arm 52 with the stationary contact 58 establishes acircuit from one side of the secondary winding 16 through conductor 96,switch blades 26 and 25, conductor 91, electric heating element '36,conductor 98, switch arm 52, contact 56, conductors 99 and 81, relaywinding 48, conductor 88, switch blades 32 and 3|, conductor 89, switch33, and conductor 98 back to the other side of the secondary winding 16.It will thus be seen that upon a call for heat by the room thermostatI0, the electric heating distance between the free ends of the twobimetallic blades I9 and I8 becomes greater and the free end of theelement I9 moves toward the safety notch 23.

Movement of the relay switch arm 53 into engagement with its stationarycontact 51 establishes a circuit from the line wire 1| through conductorI00, contact 51, switch arm 53, conductors IOI and I02, burner motor 65and conductor I03 back to the other line wire 10. This results in theenergization of the burner motor 65 which now delivers fuel to theburner. The ignition device 65 is energized simultaneously with theburner motor 65 by means of a circuit extending from the line wire 1|through conductor I00, contacts 51, switch arm 53, conductors II andI04, ignition device 66, conductor I05,

switch blades 21 and 28 and conductor I05 back to the other line wire10. The burner motor and ignition device are therefore energized at thesame time as the two electric heaters and 36.

At this time, therefore, the free end of bimetallic blade I9 is movingfarther and farther away from the free end of the bimetallic blade I8and at the end of a predetermined time interval, say seconds, it willengage in the safety notch 23 permitting the latch 20 to drop down andopen switches 25, 26; 21, 28, and3I, 32. The switch 3|, 32 is in serieswith the relay winding 48 and therefore when this switch opens the relaywill be deenergized and all of the circuits of the system will be openedand the burner motor 65 and ignition device 86 will also be deenergized.With the bimetallic blade I9 in the safety notch 23 the deenergizationof the relay winding 48 cannot result in the relatching of latch 20 bymeans of the extension 60, as explained above. Therefore, the systemremains effectively locked out until the latch 20 is repositioned bymeans of the manual reset button 62. It will be appreciated thatapplicant's showing is quite diagrammatic and that actually some meanswill have to be provided for permitting the end 6| of the latch 20 topass the extension 60 during the relatching operation to permit theparts to return to the position shown in the drawing. Any one of anumber of obvious expedients for accomplishing this purpose may be used.

Normally combustion will be established before the blade I9 enters thesafety notch 23. Under these circumstances, the combustion responsivedevice 81 will cause the switch arm 68 to engage the stationary contact69 which will establish a circuit from'on side of the secondary 16through conductor 80, contact l4, switch blade I2, bimetallic element II, conductor 92, contact 54, switch arm 50, conductors 82 and I08,contact 69, switch arm 68, conductor I09, electric heating element 31,conductor 09, switch arm 52, contact 56, conductors 99 and 81, relaywinding 48, conductor 88, switch blades 32 and 3|, conductor 83, switch63. and conductor 90 back to the other side of secondary winding 16. Itwill be noted that the establishment of this, circuit results in thesupply of additional heat from the electric heating element 31 to thebimetallic blade I8 and that this blade will now be heated to a greaterextent than the blade I9, thereby causing the free end of the blade i8to approach the blade I8 50 that after the elapse Of a predeterminedperiod of time the free end of the blade I9 will slip into the runningnotch 22 of the latch 20. Before blade I9 slips into the running notch22 however, the two blades I8 and I9 will approach sufficiently to causethe rod 45 to first force the contact blade 4| from engagement with thecontact 44. This will have no effect upon the system but as the bladesl8 and I9 come closer to each other, the stem 45 will cause the button45 on the contact blade 4| to engage the contact blade 40 and separateit from contact 43. This will deenergize the electric heater 35 andpermit the blade I! to cool. This causes it to approach the runningnotch 22 even more rapidly so that very shortly thereafter the blade 19will enter into the running notch 22 permitting the latch 20 to dropdown slightly and open switches 25, 26 and 21, 28. When'switch 25, 26opens it breaks the circuit to the electric heating element 36 so thatthe electric heating element 3! is now the only element which iseifective to heat the bimetallic blade IS. The combined effect of thetwo hea in elements 36 and 31 is suilicient to cause a fairly rapidwarping of the bimetallic blade l8 so that its operation can bedefinitely and accurately timed, but when the heating element 36 isdeenergized the effect of the heatin element 31 is to maintain thebimetallic blade l8 slightly heated so as to prevent the reclosure ofthe switches 4|, 44 and 40, 43 until the bimetallic blade I8 has cooledfor a predetermined period of time. When the bimetallic blade I! slipsinto the running notch 22, it opens switch 21, 28, as stated above, andthis results in the deenergization of the ignition device. The relaywinding 48 re-- mains energized, however, by means of a circuitextending through the combustion responsive switch 68, 68 and theelectric heating element 31. Therefore, the burner motor 65 remainsenergized. This is the running condition of the system.

The system will continue to run until the circuit to the relay winding48 is broken. This may be caused by an electrical power failure, a flamefailur causing the combustion responsive switch 68, 68 to open, or by anincrease in room temperature causing the thermostat ID to open theswitch I 2, H. In any event, the relay winding 48 will be the burnermotor 65 and to return the latch 20 to its latched position as shown inthe drawing. At this time the bimetallic blade l8 will be slightlyheated and therefore the stem 45 will be maintalning the switches 4|, 44and 40, 43 in open circuit position. After a predetermined period oftime the bimetallic blade I 8 will cool and permil; the last namedswitches to close and the parts will then have returned to the positionshown on the drawing and the system will be in condition for a restart.v

It will therefore be seen that I have designed an automatic controldevice employing a thermal timer in which heat i originally put into thetimer comparatively rapidly in order to obtain the proper timingfunction and then after the timer has moved to its running position theamount of heat put in is decreased to an amount just sufficient to holdit in running position so that the proper amount of time will be takenfor the timer to cool sufliciently to reclose the starting switchplacing the system in condition for another operation. It will be seenfurther that this thermal timing unit times the trial ignition period,the post ignition period, and the time required for the system torecycle.

As many changes and modifications of this system will doubtless occur tothose who are skilled inthe art, I wish it to be understood that Iintend to be limited only by the scope of the appended claims and not bvthe specific embodideenergized to break the circuit to ment of myinvention which has been disclosed for the purposes of illustrationonly.

I claim as my invention:

1. A fluid fuel burner control device comprising in combination, timingmeans including a timer element and a movable control element, saidtimer element and control element being relatively movable from anoriginal position for placing said control element in a running positionor safety position, said running and safety positions being on oppositesides of said original position, means controlled by circuit meansadapted to include a device responsive to a condition indicative of thedemand for heat and adapted to be associated with a fuel deliverycontrolling means for simultaneously rendering said fuel deliverycontrolling means operative and energizing said timing means to causerelative movement between said timer element and control element in adirection to place said control element in its safety position, meansoperated by said control element and adapted to be so associated withsaid fuel delivery controlling means that when said control element isin its safety position said last named means is efiective to render saidfuel delivery means inoperative, and means adapted to be connected to adevice responsive to the establishment of combustion for reversing therelative movement between said timer element and control element andcausing said control element to move to its running position providedsaid combustion responsive device is subjected to combustion conditionsbefore it has moved to its safety position.

2. A fluid fuel burner control system comprising in combination, meansfor delivering fuel to a burner, means for igniting said fuel, timingmeans including'a timer element and a movable control element, saidtimer element and control element being relatively movable from anoriginal position for placing said control element in a running positionor safety position, said running and safety'positions being on oppositesides of said original position, means operating in response to a demandfor heat for simultaneously rendering said fuel delivery means andignition means operative and energizing said timing means to causerelative movement between said timer element and control element in adirection to place said control element in its safety position, meansoperated by said control element when it is in its safety positionrendering said fuel delivery means and ignition means inoperative, meansresponsive to the establishment of combustion for reversing the relativemovement between saidtimer element and control element causing saidcontrol element to move to its running position provided combustion isestablished before it has moved to its safety position, and meansoperated by said control element when it is in its running position forrendering said ign tion means inoperative.

3. A fluid fuel burner control system comprising in combination, meansfor delivering fuel to a burner, timing means including a timer elementand a movable control element, said timer element and control elementbeing relatively movable from an original position for placing saidcontrol element in a running position or safety position, said runningand safety positions being on opposite sides of said original position,means operating in response to a demand for heat for simultaneouslyrendering said fuel delivery means operative and energizing said timingmeans to cause relative movement between said timer eletion, and meanspreventing said heat demand responsive means from rendering said fueldelivery means operative unless said control element and timer elementare in their original positions.

4. A fluid fuel burner control system comprising in combination,electrical means which, when energized, causes delivery of fuel to aburner, thermal timing means having a starting position, starting switchmeans closed by said timing means when it is in its starting position,main switch means, a starting circuit including said main switch means,starting switch means and electrical means, means responsive tocombustion operating to set up a holding circuit for said electricalmeans upon the establishment of combustion which is independent of saidstarting switch means and also operating to heat said thermal timingmeans at a relatively high rate causing said timing means to move to arunning position, and means actuated by said timing means when itreaches its running position to reduce the rate of heat supply theretoto an amount just sufficient to maintain it in its running position.

5. A fluid fuel burner control system comprising in combination,electrical means which, when energized, causes delivery of fuel to aburner, ignition means for said fuel, said electrical means alsoenergizing said ignition means, thermal timing means having a startingposition, starting switch means closed by said timing means when it isin its starting position, main switch means, a starting circuitincluding said main switch means, starting switch means and electricalmeans, means responsive to combustion operating to set up a holdingcircuit for said electrical means upon the establishment of combustionwhich is independent of said starting switch means and also operating toheat said thermal timing means at a relatively high rate causing saidtiming means to move to a running position, means operated by saidtiming means when in running position deenergizing said ignition means,and means actuated by said timing means when it reaches its runningposition to reduce the rate of heat supply thereto to an amount justsufficient to maintain it in its running position.

6. A fluid fuel burner control system comprising in combination,electrical means which, when energized, causes delivery of fuel to aburner, thermal timing means having a starting position, said thermaltiming means having two portions each tending when energized to causeeffective movement of said timing means in the opposite direction,starting switch means closed by said timing means when it is in itsstarting position, main switch means, a starting circuit including saidmain switch means, starting switch means and electrical means, means insaid starting circuit for energizing a first of said portions of saidthermal tim-lng means to cause it to move toward a safety position,means operated by said timing means when it is in its safety positionfor deenergizing said electrical means, means responsive to combustionoperating to set up a holding circuit for said electrical means which isindependent of said starting switch means, providing combustion isestablished before said timing means moves to its safety position, meansin said holding circuit for energizing the other portion of said timing,means causing it to reverse its movement and movetoward a runningposition onthe opposite side of said starting position from said safetyposition, and means actuated by said timing means when it reaches itsrunning position to reduce the rate of heat supply thereto to an amountjust sufficient to maintain it in its running position.

7. A fluidfuel burner control system comprising in combination,electrical means which, when energized, causes delivery of fuel to aburner, thermal timing means having a cold position, starting switchmeans closed by said timer in its cold position, a first heaterassociated with one portion of said timing means, second and thirdheaters associated with a second portion of said timing means, meansactuated upon a demand for heat for closing a starting circuit includingsaid starting switch means and electrical means and energizing saidfirst and second heaters, said first and second heaters causing saidthermal means to move toward a safety position in which it deener gizessaid electrical means,- means responsive to combustion for energizingsaid third heater and setting up a holding circuit for said electricalmeans independent 01' said startingswitch means providing combustiontakes place before said thermal means reaches its safety position, saidthird heater causing said thermal means to reverse its movement and moveto a running position, said thermal means opening said starting switchmeans and deenergizing said first and second heaters when itreaches'said running position, said third heater preventing reclosure ofsaid starting switch means until said third heater is deenergized uponsatisfaction of said demand for heat and said thermal means has returnedto its cold position.

8. A fluid fuel burner control system comprising in combination,electrical means which, when energized, causes delivery of fuel to aburner, ignition means for the fuel, said electrical means alsoenergizing said ignition means, thermal tim ing means having a coldposition, starting switch means closed by said timer in its coldposition, a first heater associated with one portion of said timingmeans, second and third heaters associated with a second portion of saidtiming means, means actuatedupon a demand for heat for closing astarting circuit including said starting switch means and electricalmeans and energizing said first and second heaters, said first" andsecond heaters causing said thermal means to move toward a safetypositionin'which it deenergizes said electrical means, means responsiveto combustion for energizing said third heater and setting up a holdingcircuit for said electrical means independent of said startingswitch'means providing combustion takes place before said thermal meansreaches its safety position, said third heater causing said thermalmeans to reverse its movement and move to a running position, saidthermal means opening said starting switch means, deenergizing saidignition means, and deenergizing said first and second heaters when itreaches said running position, said third heater preventing reclosure ofsaid starting switch means until said third heater is deenergizeduponsatisfaction of said demand for'heat and said thermal means has returnedto its cold position.

9. A fluid fuelburner control device comprising inv combination, anelectric relay which is adapted to be connected to means for controllingthe delivery of fue1 to a burner and which is adapted when so connectedand when energized to render said means operative to deliver fuel, alatch having a latching surface and a running notch, thermal timingmeans including a member which engages said latching surface in the coldposition of said thermal means, starting switch means closed by saidthermal means in its cold position, circuit means adapted to beconnected to a main switch means and when 50 connected to form astarting circuit including said main switch means, starting switch meansand relay, further circuit mean adapted to be connected to a deviceresponsive to the establishment of combustion for establishing a holdingcircuit for said relay and heating said thermal means at a relativelyrapid rate thus causing said member to move into said running notch,said thermal means opening said starting switch, means operated by saidlatch when said member moves into said running notch for reducing therate of heating said thermal means, the opening of said main switchmeans causing deenergization of said relay and termination of theheating of said thermal means, and means operated by said relay upondeenergization thereof for relatching said latch on said member.

10.-A'fluid fuel burner control system comprising in combination, meansfor delivering fuel to a burner, means to ignite said fuel, an electricrelay which, when energized, energizes said ignition means and renderssaid means operative to deliver fuel, a latch having a latching surfaceand a running notch, thermal timing means including a member whichengages said latching surface in the cold position of said thermalmeans, starting switch means closed by said thermal means in its coldposition, main switch means,

a starting circuit including said main switch means, starting switchmeans and relay, means responsive to the establishment of combustionestablishing a holding circuit for said relay and heating said thermalmeans at a relatively rapid rate thus causing said member to move intosaid running notch, said thermal means opening said starting switch,means operated by said latch when said member moves into said runningnotch for deenergizing said ignition means and reducing the rate ofheating said thermal means, the opening of said main switch meanscausing deenergization of said relay and termination of the heating ofsaid thermal means, and means operated by said relay upon deenergizationthereof for relatching said latch on said member.

11. A fluid fuel burner control system comprising in combination, meansfor delivering fuel to a burner, an electric relay which, whenenergized, renders said means operative to deliver fuel, a latch havinga latching surface, a safety notch and a running notch, thermal timingmeans including a member which engages said latching surface in the coldposition of said thermal means, starting switch means closed by saidthermal means in its cold position, main switch means,

.a starting circuit including said main switch means, starting switchmeans and relay, heating means rendered operative by said startingcircuit for causing said member to move into said safety notch after apredetermined period of time, meansoperated by said latch when saidmember has moved into said safety notch for deenergizing said relay,means responsive to the establishment lished before said member movesinto said safety notch, for establishing a holding circuit for saidrelay and heating said thermal means at a relatively rapid rate thuscausing said member to move into said running notch, said thermal meansopening said starting switch, means operated by said latch when saidmember moves into said running notch for reducing the rate of heatingsaid thermal means, the opening of said main switch means causingdeenergization of said relay and termination of the heating of saidthermal means, and means operated by said relay upon deenergizationthereof for relatching said latch on said member, said last named meansbeing inoperative to relatch said latch when said member is in saidsafety notch.

12. A fluid fuel burner control system comprising in combination, meansfor delivering fuel to of combustion, providing combustion is estab- 7 aburner, means to ignite said fuel, an electric relay which, whenenergized, energizes said ignition means and renders said meansoperative to deliver fuel, a latch having a latching surface, a safetynotch and a running notch, thermal timing means including a member whichengages said latching surface in the cold position of said thermalmeans, starting switch means closed by said thermal means in its coldposition, main switch means, a starting circuit including said mainswitch means, starting switch means and relay, heating means renderedoperative by said starting circuit for causing said member to move intosaid safety notch after a predetermined period of time, means operatedby said latch when said member has moved into said safety notch fordeenergizing said relay, means responsive to the establishment ofcombustion, providing combustion is established before said member movesinto said safety notch, for establishing a holding circuit for saidrelay and heating said thermal means at a relatively rapid rate thuscausing said member to move into said running notch, said thermal meansopening said starting switch, means operated by said latch when saidmember moves into said running notch for deenergizing said ignitionmeans and reducing the rate of heating said thermal means, the openingof said main switch means causing deenergization of said relay andtermination of the heating of said thermal means, and means operated bysaid relay upon deenergization thereof for relatching said latch on saidmember, said last named means being inoperative to relatch said latchwhen said member is in said safety notch.

13. A fluid fuel burner control system comprising in combination, meansfor delivering fuel to a burner, an electric relay which, whenenergized, renders said means operative to deliver fuel, a latch havinga latching surface, a safety notch and a running notch, thermal timingmeans including a member which engages said latching surface in the coldposition of said thermal means, a first heater associated with oneportion of said thermal means, second and third heaters associated withanother portion of said thermal means, starting switch means closed bysaid thermal means in its cold position, means responsive to a demandfor heat establishing a starting circuit for said relay including saidstarting switch means, the closure of said circuit resulting in theenergization of said first and second heaters which cause said member tomove into said safety notch after a predetermined period of time, meansoperated by said latch when said member is in said safety notch fordeenergizing said relay and heaters, means responsive to combustion,providing combustion is established before said member moves into saidsafety notch, for setting up a holding circuit for said relayindependent of said starting switch means, and energizing said thirdheater causing the relative movement between said member and latch toreverse whereby said member moves into said running notch, meansdeenergizing said first and second heaters when said member is in saidrunning notch, said heat demand responsive means deenergizing said relayand third heater when said heat demand is satisfied, and means operatedby said relay upon deenergization thereof for relatching said latch ifsaid member is in said running notch but not if it is in said safetynotch.

14. A fluid fuel burner control system comprising in combination, meansfor delivering fuel to a burner, means to ignite said fuel, an electricrelay which, when energized, energizes said ignition means and renderssaid means operative to deliver fuel, a latch having a latching surface,a safety notch and a running notch, thermal timing means including amember which engages said latching surface in the cold position of saidthermal means, a first heater associated with one portion of saidthermal means, second and third heaters associated with another portionof said thermal means, starting switch means closed by said thermalmeans in its cold position, means responsive to a demand for heatestablishing a starting circuit for said relay including said startingswitch means, the closure of said circuit resulting in the energizationof said first and second heaters which cause said member to move intosaid safety notch after a predetermined period of time, means operatedby said latch when said member is in said safety notch for deenergizingsaid relay and heaters, means responsive to combustion, providingcombustion is established before said member moves into said safetynotch, for setting up a holding circuit for said relay independent ofsaid starting switch means, and energizing said third heater causing therelative movement between said member and latch to reverse whereby saidmember moves into said running notch, means deenergizing said first andsecond heaters and said ignition means when said member is in saidrunning notch, said heat demand responsive means deenergizing said relayand third heater when said heat demand is satisfied, and means operatedby said relay upon deenergization thereof for relatching said latch ifsaid member is in said running notch but not if it is in said safetynotch.

15. An intermittent ignition system for a fluid fuel burner comprisingin combination, means for delivering fuel to a burner, means to ignitesaid fuel, an electric relay which, when energized, renders said fueldelivery and ignition means operative, a thermal timer including a latchhaving a latching surface and a running notch and a member cooperablewith said latch and movable relatively thereto, means energizing saidrelay in response to a demand for heat, means responsive to combustionfor energizing said timer to cause said member to move into said runningnotch, means operable by said latch when said member is in said runningnotch for deenergizing said ignition means, and means operable by saidrelay upon deenergization thereof for relatching said latch.

16. An intermittent ignition system for a fluid fuel burner comprisingin combination, means for delivering fuel to a burner, means to ignitesaid fuel, an electric relay which, when energized, renders said fueldelivery and ignition means operative, a thermal timer including a latchhaving a latching surface, a safety notch andva running notch, and amember cooperable with said latch and movable relatively thereto, meansenergizing said relay in response to a demand for heat and alsoenergizing said thermal timer in a manner to cause said member to moveinto said safety notch after a predetermined period of time, meansoperated when said member is in said safety notch for deenergizing saidrelay, means responsive to combustion, provided combustion isestablished before said member moves into said safety notch, forenergizing said thermal timer in a manner to cause said member to moveinto said running notch, means operable by said latch when said memberis in said running notch for deenergizing said ignition means, meansoperable by said relay upon deenergization thereof for relatching saidlatch if said member is in said running notch but not if it is in saidsafety notch, and manual means for relatching said latch when saidmember is in said safety notch.

17. An intermittent ignition system for a fluid fuel burner comprisingin combination, means for delivering fuel to a burner, means to ignitesaid fuel, an electric relay which, when energized, renders said fueldelivery and ignition means operative, a thermal timer including a latchhaving a latching surface and a running notch and a member cooperablewith said latch and movable relatively thereto, starting switch means,means closing said starting switch means when said latch is latched andopen when said member is in said running notch, means energizing saidrelay in response to a demand for heat, said last named means includingsaid starting switch means, means responsive to combustion forenergizing said timer to cause said member to move into said runningnotch, means operable by said latch when said member is in said runningnotch for deenergizing said ignition means and reducing the energizationof said thermal timer, means operable by said relay upon deenergizationthereof for relatching said latch, and means terminating energization ofsaid thermal timer upon deenergization of said relay, said timerreclosing said starting switch means after a predetermined time.

18. A fluid fuel burner control system comprising in combination, meansfor delivering fuel to a burner, a timer unit having a startingcondition, asafety condition, and a running condition, means responsiveto a demand for heat for rendering said fuel delivery means operative,means preventing said heat demand responsive means from rendering saidfuel delivery means operative except when said timer unit is in itsstarting condition, said timer means being energized substantiallysimultaneously with said fuel delivery means for movement to its safetycondition, means rendering said fuel delivery means inoperative whensaid timer unit is in its safety condition, means responsive to theestablishment of combustion, providing combustion is established toreduce the energization of said timer unit to a continuous amount justsufficient for it to have the proper timing on returning to its startingcondition following a deenergiz'ation thereof by said heat demandresponsive means.

19. A fluid fuel burner control system comprising in combination, meansfor delivering fuel to a burner, means for igniting said fuel, a timer 5unit having a starting condition, a safety conditlon. and a runningcondition, means responsive to a demand for heat for rendering said fuelde livery means and said ignition means operative,

means preventing said heat demand responsive 10 timer unit is in itssafety condition, means responsive to the establishment of combustion,providing combustion is established before said timer unit moves to itssafety condition, for continuously energizing said timer unit in amanner to move to its running condition and to maintain said fueldelivery means operating independently of said timer unit, meansoperated by said timer unit in its running condition to deenergize saidignition means and to reduce the energization of said timer unit to acontinuous amount just sufficient for it to have the proper timing onreturning to its starting condition following a deenergization thereofby said heat demand re- 15 sponsive means.

SIEGFRIED G. ISSERSTEDT.

